GB/T 31776-2015 Test method for the determination of methanol content in methanol gasoline for motor vehicles

Summary page. This page is a compiled excerpt/summary of the standard — it is not the full standard text and does not replace it. Verify every value against the official standard and the product certificate before use.

GB/T 31776-2015 specifies the method for determining the methanol content of methanol gasoline for motor vehicles; this page covers the scope and ethanol precondition, the chromatographic principle, reagents and conditions, calibration, calculation and permissible differences.

Evidence note: original compilation based on the 2015 edition, not the full text of the standard or a controlled operating procedure, and technical review is pending. The identification of ethanol, the choice of sample volume and the unverified procedures are kept separate, and no product applicability is inferred.

Method identity and version: Original PDF 1–3; official version record. GB/T 31776-2015, Test method for the determination of methanol content in methanol gasoline for motor vehicles. The cover states an issue date of 2015-07-03 and an implementation date of 2015-10-01. The standard is administered by the National Technical Committee for Standardisation of Alcohol Ether Fuels. As read on 2026-10-10, the two official services show it as current, and the detailed record shows the review conclusion of 2025-11-03 as continued validity. Verification of official metadata and technical review of the original are separate; this page does not thereby confirm a particular contract, the accreditation scope of a laboratory or product applicability.

Scope and the ethanol precondition: Original PDF 4, clause 1 and PDF 6, clause 8.3. This edition determines methanol in ethanol-free methanol gasoline for motor vehicles, the result being the methanol volume fraction. Ethanol is the internal standard used for quantitation, so the sample is first checked for ethanol. Original 8.3 suggests an external-standard method for samples containing ethanol, but that page does not give a complete external-standard calibration procedure or the corresponding permissible differences, so the internal-standard quantitation of this page cannot be applied directly. A study page is not a controlled operating procedure and does not cover all samples the original does not describe.

Principle and detection signal: Original PDF 4, clause 4 and 5.1. The sample, the ethanol internal standard and a measured amount of distilled water are mixed under the specified conditions so that methanol and ethanol pass into the aqueous layer; after separation the aqueous phase is analysed, with separation on a Porapak T packed column and detection by a hydrogen flame ionisation detector (FID), quantitation by internal standard using peak area ratios. The original figure specifies a hydrogen flame; "oxygen flame" in the OCR must not be taken as fact. Peak area, retention time and the final methanol volume fraction are different quantities and do not substitute for one another.

Apparatus and chromatographic column: Original PDF 4–5, clause 5 and 6.11. The chromatograph is fitted with an FID and meets the sensitivity and stability requirements of GB/T 9722 as cited in this edition, and the workstation matches the instrument. The Porapak T packed column is 1 m long with an internal diameter of 3 mm; the micro-syringe capacity is 1 μL, which is not the actual injection volume. The packing is 60–80 mesh, with 2 cm left at each end of the column and filled with glass wool; before use the column is aged at an oven temperature of 180 °C until the baseline is stable. The construction of the components and the complete safe operation have not been reconstructed, and this is not a basis for equipment manufacture or direct operation.

Typical chromatographic conditions: Original PDF 5, Table 1. The following are typical conditions of this edition; the original permits other working conditions giving an equal or better analytical result, and the actual equivalent analytical capability must be verified — a temperature change alone does not make a configuration suitable. The 0.5 μL injection volume is separate from the 1 μL syringe capacity. Temperature and gas flow rates are method conditions, not a basis for product storage. Item | Typical condition Detector temperature | 200 °C Oven temperature | 150 °C Inlet temperature | 200 °C Nitrogen flow | 30 mL/min Hydrogen flow | 30 mL/min Air flow | 300 mL/min Injection volume | 0.5 μL

Reagents, gases and containers: Original PDF 5, clause 6. Anhydrous methanol and anhydrous ethanol are of chromatographic grade; the component oil is selected according to GB 17930 or GB/T 22030 as cited in this edition. The carrier gas nitrogen and the fuel gas hydrogen have a purity of not less than 99.99 % (volume fraction); the air is supplied by an air generator. This edition lists a 250 mL pear-shaped separating funnel and various measuring devices. Distilled water, the ethanol internal standard and the calibration methanol serve different purposes; no product catalogue number, certificate value or supply relationship is added. The reference record does not mean that the current version of every referenced document has been checked.

Sampling, storage and phase separation: Original PDF 5–6, clause 7 and 8.1. Take 2 L for testing and retention following the GB/T 4756 procedure cited in this edition; the sample is stored at 0 °C–5 °C; before analysis it is shaken thoroughly and observed for phase separation, and a sample showing obvious phase separation is discarded and a new one taken. At analysis, the sample, internal standard, distilled water and measuring vessels must be equilibrated at a certain temperature before use. The original clause does not give the numerical value of that equilibration temperature, and it is not guessed here. The sample storage temperature is not the keeping or opening condition of any particular product.

Identification of ethanol in the original sample: Original PDF 6, clause 8.3 and PDF 7–8, Figures 1–2. The identification test uses 100 mL of distilled water and 60 mL of the original sample, shaken for 4 min and left to separate for 6 min; 0.5 μL of the aqueous phase is then analysed and checked for ethanol against the chromatogram of this edition. The 6 min standing here differs from the 8 min used in the later calibration and sample quantitation and must not be confused. Only an ethanol-free sample enters the internal-standard procedure of this page; the external-standard suggestion for samples containing ethanol cannot be regarded as a validated complete alternative method.

Linearity check: Original PDF 6, clause 8.4. Using 100.0 mL of distilled water and 4.00 mL of ethanol internal standard with six methanol additions: 0.10, 0.30, 0.50, 1.00, 3.00 and 5.00 mL; 0.5 μL of each aqueous phase is analysed and the peak area ratio F of methanol to internal standard is recorded. F is plotted on the ordinate against the methanol addition on the abscissa; the original criterion is a correlation coefficient greater than 0.999, which must not be changed to greater than or equal to. It is a check of system linearity, not a sample detection limit or a promise of product purity.

Calibration and the corresponding sample volume: Original PDF 6, Table 2 and 8.5; PDF 7, Table 3. Calibration samples of known volume fraction M are prepared from methanol and component oil. The sample volume N for calibration and for the sample to be tested corresponds as in Tables 2 and 3 of this edition; the two tables give the same five sets of values. The original gives no continuous interpolation rule for arbitrary concentrations, and no automatic calculator is published on this page. Calibration uses 100.0 mL of water, the calibration sample of the corresponding N and 4.00 mL of ethanol internal standard, shaken for 4 min and left to separate for 8 min, with 0.5 μL of the aqueous phase; three parallel injections are made and the mean peak area ratio of methanol to internal standard, F_s/int, is taken. Methanol volume fraction M/% | Sample volume N/mL for calibration and test 5 (5.0 in Table 2) | 60.0 15 (15.0 in Table 2) | 20.0 30 (30.0 in Table 2) | 10.0 50 (50.0 in Table 2) | 6.0 85 (85.0 in Table 2) | 3.5

Sample quantitation and identification: Original PDF 7, clauses 8.6–8.8 and Table 4. The sample to be tested uses 100.0 mL of water, the sample volume N corresponding to Table 3 and 4.00 mL of ethanol internal standard, shaken for 4 min and left to separate for 8 min; 0.5 μL of the aqueous phase is injected and the peak area ratio of methanol to internal standard, F_i/int, is obtained. Each sample is determined twice in parallel; the three injections of the calibration must not be used to rewrite the number of sample determinations. The heading of original Table 4 says relative retention time and gives the unit min; this page retains that record, does not reinterpret it as a dimensionless ratio, and does not treat the example times as necessarily identical on all instruments. The peak diagrams of original Figures 1–2 have not been fully reconstructed. Component | Sample record /min | Reference material record /min Methanol | 0.91 | 0.89 Ethanol internal standard | 2.07 | 2.04

Calculation of results and reporting: Original PDF 8, clause 9, equation 1: X = (F_i/int ÷ F_s/int) × M. X is the methanol volume fraction of the sample (%), M the methanol volume fraction of the calibration sample corresponding to sample volume N (%); F_s/int is the peak area ratio of the calibration sample and F_i/int that of the sample to be tested. The arithmetic mean of two duplicate determinations is taken, kept to one decimal place. The correspondence between different values of N must not be ignored; this page provides no calculator for results on an actual instrument and no acceptance decision for a particular product.

Permissible differences and interpretation boundaries: Original PDF 8, clause 10, Table 5. The original clause requires the absolute difference between parallel calculation results to comply with the table below; an absolute difference in volume fraction % must not be interpreted as a relative percentage error or as batch certificate uncertainty. The original table is titled permissible difference of repeatability test results and lists values for the same and for different laboratories; this page keeps both columns and does not extend them to a universal reproducibility for arbitrary samples. The clause gives no 95 % confidence level, and none is guessed. Methanol volume fraction M/% | Absolute difference, same laboratory /% | Absolute difference, different laboratories /% M ≤ 30 | 0.30 | 0.40 30<M<85 | 0.40 | 0.50 M ≥ 85 | 0.50 | 0.60

Sources, discrepancies and common questions: Original PDF 1–9 and official records. The nine physical pages are, in order, the cover, contents, foreword, printed body pages 1–5 and the publication page; figures, tables and formulas were located against the original images, with OCR used only for searching. Clause 2 refers to GB/T 4756, GB/T 9722, GB 17930 and GB/T 22030, and the current referenced versions and their specific applicability must be checked separately. Why check for ethanol first? It affects the precondition for internal-standard quantitation with ethanol; the complete external-standard steps for samples containing ethanol are not provided on this page. Are calibration and samples both injected three times? No — calibration uses three injections, samples two determinations. Can the permissible difference be used as certificate uncertainty? No. The items awaiting verification include the choice of sample volume for concentrations not listed, the specific equilibration temperature, the external-standard procedure and permissible differences, the complete chromatograms and the controlled safe operation. Compiling the original is not the same as completing independent technical acceptance; the original scans are not published and product relationships are not guessed.

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